It is well known to those skilled in the art that nonionic surfactants are useful in formulating laundry detergents for use in low water temperature washes. It is further known that nonionic surfactants are particularly efficient at removing oily soils from synthetic fabrics but that they are not as efficient at removing particulate soils as anionic surfactants. As a result it is desirable to include detergent builders in detergent formulations containing nonionic surfactants to improve performance on particulate soils and provide good overall cleaning performance.
Nonionic surfactants are typically combined with builders by spray-drying or agglomeration processes to make dry powdered detergents. However, the amount of nonionic surfactant that can be included in such powder detergents is limited by the amount that can be absorbed into or adsorbed onto the solid components. Agglomeration techniques usually produce dense particles that have limited capacity for absorbing nonionic surfactants and the final compositions can have poor solubility rates and flowability. Spray-drying techniques produce more porous particles that can sorb more nonionic surfactant. However, the temperatures involved in spray-drying can cause decomposition of the nonionic surfactant and it is desirable to add the nonionic surfactant in a second step if a high concentration is desired. Since the spray-drying process is energy and capital intensive, this approach results in high manufacturing costs. In addition, if certain builders are present, the spray-drying process itself can lead to the formation of insoluble particles that deposit on clothes during the washing process. In spray-drying processes, slurries are utilized which may contain builders and nonionic surfactants, but with a high amount of water (usually around 30-70%). Such slurries would themselves be unacceptable as detergents since they will have long term phase stability problems and will deliver only diluted amounts of active ingredients and the high level of water can cause chemical stability problems.
High levels of nonionic surfactants can be readily incorporated into liquid laundry detergents. However, these formulations are normally severely limited in the type and amount of builder that can be incorporated therein since the builder must be soluble or dispersible in the formulation to prevent phase separation. As a result, the overall particulate soil removal performance of liquid laundry detergents is generally poorer than that of powder detergents.
There have been attempts to combine high levels of nonionic surfactants and builders in laundry detergent formulations which have the physical form of mulls or pastes. U.S. Pat. No. 4,264,466, issued to Carleton et al, describes detergent mulls which contain chain structure clays to prevent phase separation of the liquid and solid components. Carleton et al contend that poor phase stability results if chain structure clays are omitted from their formulations. However, chain structure clays can hinder solubility of detergent compositions.
Because of the viscous nature of these paste formulations, it is difficult to deliver them into the washing machine from a conventional, liquid laundry detergent bottle, even one equipped with a pump dispenser. The use of a squeezable tube, similar to those used to dispense toothpaste, to dispense a detergent in the form of a paste may be feasible from a technical consideration, but the size of the tube required to contain a reasonable amount o detergent for multiple wash loads would make it difficult for the consumer to use conveniently.
The use of pouches constructed of water soluble films to deliver unit dosages of laundry additives is well documented. However, there has been no demonstration in the prior art of the use of such pouches to contain and deliver a composition containing a high level of nonionic surfactant. For example, U.S. Pat. No. 4,115,292, issued to Richardson et al, shows compositions with low amounts of very high pour point nonionic surfactants and relatively high amounts of water in water-soluble polyvinyl alcohol pouches.
From cleaning performance considerations, inorganic phosphates are the first choice as builders in detergent compositions. However, phosphates have been implicated in polluting lakes and streams since they promote algal growth, leading to eutrophication of free standing waters. As a result, there has been substantial legislation promulgated which restricts the use of phosphates in laundry detergents in the United States and other countries.
Sodium aluminosilicates (zeolites) have been shown to be acceptable replacements for phosphates in laundry detergent compositions. However, to be effective, they must have a particle size which is less than about 10 microns and thus, can lead to dispersibility/solubility problems, especially in compositions in the form of pastes. Solubility problems may occur because of the interactions among these particles throughout the detergent matrix.
U.S. Pat. No. 4,409,136, issued to Cheng, describes viscous pastes containing nonionic surfactant, zeolite builders and a high amount of water (at least 10% water added in addition to that contained in the zeolite; the Cheng disclosure states however, that preferably at least 25% water is added). Because of the high amount of water, these pastes will not deliver concentrated amounts of detergents in the wash water. Further, as will be disclosed in detail later, these compositions are not formulated to provide good solubility in cool and cold water washes. Also, it is desirable to include enzymes in laundry detergent compositions and it is known that the addition of water to such compositions can have negative effects on enzyme stability.
Other non-phosphate builders such as citrates, silicates and carbonates have also been used in laundry detergent compositions, but formulations based on these builders are generally less efficacious than those based on phosphates or zeolites. Further, the alkaline nature of carbonates and silicates can have deleterious effects on polyvinyl alcohol films used to package these detergents.